It is well known that various hydrocarbon oils have to be upgraded before they meet the particular specification set for them. Usually, hydrocarbon oils obtained by various (hydro)processes need to be upgraded to remove undesired materials which were either present in the starting material(s) or have been introduced during one or more steps of the treatment leading to the desired products.
One of the upgrading processes often applied in hydrocarbon oil processing comprises hydrogenation, often referred to as hydrofinishing. A well known hydrogenation catalyst capable of removing substantially unsaturated moieties such as olefinic compounds and in particular aromatic compounds by converting them into the corresponding saturated compounds comprises a noble metal catalyst on an amorphous carrier, such as platinum on silica-alumina. Although such catalysts show a very good performance as regards hydrogenation activity, they are rather sensitive to the presence of sulphur and/or nitrogen compounds in the feedstock to be treated. In commercial operation preferably hydrotreated feedstocks are used which have sufficiently low sulphur and nitrogen levels to allow an acceptable catalyst life time.
It is known from U.S. Pat. No. 3,943,053 to use a hydrogenation catalyst containing both platinum and palladium in a specific molar ratio, preferably using an alumina carrier. It is emphasized in said patent specification that the use of silica-alumina carriers easily leads to different and undesired reactions thus substantially reducing the yield of the desired product. The advantage of the use of both platinum and palladium resides in an increased sulphur and nitrogen resistance. It also appears necessary to use simultaneous impregnation of the carrier with both platinum and palladium salts in the same acidic solution. Subsequent impregnation of either metal salt is reported not to yield suitable catalyst.
It should be noted that zeolitic materials having high SiO.sub.2 /Al.sub.2 O.sub.3 structural ratios are known to be active hydrocracking catalysts. Reference is made in this respect to EP-B No. 98040 wherein hydrocracking catalysts are described based on highly siliceous forms of certain large pore zeolites (Y,ZSM-20 and beta) comprising typically Ni, W, rare earth metals and Mg as active metal components. It is stated in said patent specification that a preliminary hydrotreating step to remove sulphur and nitrogen and to saturate aromatics to naphthenes will usually improve (hydrocracking) catalyst performance. The use of a Group VIII metal on ZSM-20 as hydrocracking catalyst is also described in U.S. Pat. No. 4,377,468.
It has now been found that the use of certain noble metal(s)-containing zeolitic materials allows very good hydrogenation of feedstocks containing in particular aromatic unsaturation. By the proper choice of zeolitic material and using platinum and in particular platinum and palladium as noble metal(s) a very high hydrogenation yield can be obtained without being affected under operating conditions by substantial hydrocracking.